Originally Posted by
corporate-wage-slave
I suspect at some point any second proof of identity would be OK. Though the ground agents would have felt this was a necessary thing to do, they would also know that there would be problems for them if they denied travel to someone incorrectly. I've not come across where there was a claim for IDB in this scenario.
I mean, never known ground agents to care much about unnecessarily denying travel. Since the punishment for incorrectly boarding pax is significantly higher than the (virtually non-existent) punishment for IDB, I would be willing to bet that they are far more likely to incorrectly deny boarding than to incorrectly permit boarding. Airlines love to make up rules, like requiring a return flight for places that don't require it or requesting visas you can receive on arrival.
As far as accepting any second proof of identity, is this a requirement to visit the US? Fairly certain I have never been asked such a thing. (I know plenty of people without driving licences, and plenty of people without any second proof of identity.) Even if I happened to be carrying my driving licence, I would probably not want to show it just because the idea of requiring passengers to be able to drive as a condition to board a flight seems rather outrageous.